Field of the Invention
Embodiments of the present invention relate to feedthroughs and connectors for optical waveguides and, more particularly, to monolithic multi-optical-waveguide feedthroughs and connectors.
Description of the Related Art
In many industries and applications, there is a need to have electrical wires or optical waveguides penetrate a wall, bulkhead, or other feedthrough member wherein a relatively high fluid differential pressure exists across the feedthrough member. In addition, one or both sides of the feedthrough member may be subjected to relatively high temperatures and other harsh environmental conditions, such as corrosive or volatile gas, liquids, and other materials.
Recently, with the introduction of optical sensors, particularly sensors for use in oil and gas exploration and production and for deployment in harsh industrial environments, a need has emerged for a bulkhead feedthrough that can seal an optical fiber at high pressures of 20,000 psi and above, and high temperatures of at least 150° C. to 300° C., with a service life of at least 5 to 20 years.
There are several problems associated with constructing such an optical fiber feedthrough. One of these problems is the susceptibility of the glass fiber to damage and breakage. This is due to the flexibility of the small diameter fiber, the brittle nature of the glass material, and the typical presence of a significant stress concentration at the point where the fiber enters and exits the feedthrough. Attempts to use a sealing glass, such as that used with electrical feedthroughs, have had problems of this nature due to the high stress concentration at the fiber-to-sealing glass interface.
Another problem with sealing an optical fiber, as opposed to sealing a conductive metal “pin” in an electrical feedthrough, is that the fused silica material of which the optical fiber is made, has an extremely low thermal expansion rate. Unlike most engineering materials—including metals, sealing glasses, as well as the metal pins typically used in electrical feedthroughs—the coefficient of thermal expansion of the optical fiber is essentially zero. This greatly increases the thermal stress problem at the glass-to-sealing material interface.
As discussed above, the harsh environments where the sensors are located generally must be isolated by sealed physical barriers from other proximate environments through which the optical fiber communication link of the sensor must pass. It is important to seal the bulkhead around the optical fiber to prevent environments adjacent to the sensor from contaminating the optical fiber communication link. If the optical communication fiber is compromised by contamination from an adjacent harsh environment, the optical fiber and all sensors to which it is connected are likely to become ineffective.
An exemplary sensing assembly for use in harsh environments is disclosed in U.S. Pub. No. 2007/0003206 to Dunphy et al., entitled “Optical Waveguide Feedthrough Assembly,” which is assigned to the Assignee of the present application and is incorporated herein by reference in its entirety. Dunphy discloses the optical waveguide feedthrough assembly of FIG. 1. The assembly 100 includes a front housing 10 coupled to a back housing 12. An optical waveguide element 14 passes through a passageway 16 common to both housings 10, 12. The passageway 16 is defined by bores extending across the housings 10, 12. The optical waveguide element 14 includes a glass plug 18 defining a large-diameter, cane-based, optical waveguide preferably having an outer diameter of about 3 millimeters (mm) or greater. The glass plug 18 can have appropriate core and cladding dimensions and ratios to provide the desired outer large-diameter.
First and second fiber pigtails 19, 20 extend from each end of the glass plug 18. Each of the pigtails 19, 20 includes an optical waveguide such as an optical fiber 26 encased or embedded in a carrier 28 or larger diameter glass structure allowing the fiber 26 to be optically coupled to the glass plug 18. Sealing of the optical waveguide element 14 with respect to the front housing 10 occurs at and/or around the glass plug 18 to enable isolation of fluid pressure in communication with a first end 22 of the passageway 16 from fluid pressure in communication with a second end 24 of the passageway 16. This sealing of the glass plug 18 with respect to the front housing 10 provides the feedthrough capabilities of the feedthrough assembly 100. The glass plug 18 has a cone-shaped tapered surface 50 for seating against a complementary tapered seat 51 of the front housing 10. Engagement between the tapered surface 50 and the complementary tapered seat 51 that is located along the passageway 16 forms a seal that seals off fluid communication through the passageway 16. The glass plug 18 can be machined to provide the cone-shaped tapered surface 50. Additionally, the glass plug 18 is preferably biased against the tapered seat 51 using a mechanical preload.
A recess 30 formed in one end of the front housing 10 aligns with a corresponding recess 31 in one end of the back housing 12 where the housings 10, 12 are coupled together. Preferably, the front housing 10 is welded to the back housing 12 along mated features thereof. The housings 10, 12 preferably enclose the glass plug 18, a biasing member such as a first stack of Belleville washers 34, and a plunger 32, which are all disposed within the recesses 30, 31.
The first stack of Belleville washers 34 supply the mechanical preload by pressing the plunger 32 onto an opposite end of the glass plug 18 from the tapered surface 50. Since the plunger 32 is moveable with the glass plug 18, this pressing of the plunger 32 develops a force to bias the glass plug 18 onto the tapered seat 51 of the front housing 10 located along the passageway 16 that passes through the front housing 10. Transfer of force from the plunger 32 to the glass plug 18 can occur directly via an interface 54 between the two, which can include mating conical surfaces. The first stack of Belleville washers 34 compresses between a base shoulder 44 of the recess 31 in the back housing 12 and an outward shoulder 46 of the plunger 32 upon make-up of the front housing 10 to the back housing 12. Once the back housing 12 is welded or otherwise attached to the front housing 10 in order to keep the front and back housings 10, 12 connected, the first stack of Belleville washers 34 maintains the compression that supplies force acting against the plunger 32.
The feedthrough assembly 100 further includes a gasket member 52 disposed between the tapered seat 51 and the tapered surface 50 of the glass plug 18. The gasket member 52 comprises an annular gasket. The gasket member 52 may be a gold foil that is shaped to complement the tapered surface 50 and the tapered seat 51. The gasket member 52 deforms sufficiently to accommodate imperfections on the tapered surface 50 and/or the tapered seat 51, thereby completing the seal and reducing stress between contacting surfaces due to any imperfections on the surfaces.
The housings 10, 12 additionally enclose a cup-shaped backstop sleeve 36, a second stack of Belleville washers 38, a perforated washer 40, and a centering element 42 that are all disposed within the recesses 30, 31. An outward shoulder 56 of the backstop sleeve 36 is trapped by the end of the front housing 10 and an inward shoulder 57 along the recess 31 in the back housing 12. Contact upon sandwiching of the shoulder 56 of the backstop sleeve 36 provides the point at which the housings 10, 12 are fully mated and can be secured together. Clearance is provided such that the end of the back housing 12 does not bottom out prior to the housings 10, 12 being fully mated.
The centering element 42 includes an elastomeric sealing component disposed between the glass plug 18 and the front housing 10 that can act as a back-up seal in addition to facilitating alignment of the glass plug 18 with respect to the seat 51. The pressure in the recesses 30, 31 entering from the second end 24 of the passageway 16 is higher than the pressure entering from the first end 22 of the passageway 16. This pressure differential advantageously causes the centering element 42 to deform and press against the wall of the recess 30 and the wall of the glass plug 18, thereby creating a pressure-energized seal. One or more holes or annular channels 43 can be formed on the outer surface of the high pressure side of the centering element 42. These holes or channels 43 facilitate the deformation of the centering element 42 and the formation of the seal between the centering element 42 and the walls of the recess 30 and the glass plug 18. Additionally, the perforated washer 40 enables pressurized fluid to fill the centering element 42 for providing the energized seal.
Preferably, force transferred through the perforated washer 40 biases the centering element 42 into the recess 30. The second stack of Belleville washers 38 pressed by the backstop sleeve 36 supplies the preloading force to the perforated washer 40. The second stack of Belleville washers 38 allow a maximum pressure force to act on the centering element 42 such that pressure of the centering element 42 against the wall of the glass plug 18 does not override force being put on the glass plug 18 to press the tapered surface 50 against the seat 51.
The assembly 100 is suited for feedthrough of a single optical waveguide. If feedthrough of multiple waveguides is desired, a separate assembly may be used for each individual waveguide. This means additional costs and additional space requirements on a production tree, for example.
Accordingly, there is a need for an optical waveguide feedthrough assembly capable of operating in relatively high temperature and high pressure environments in which multiple optical waveguides are fed through.